1. Field of the Invention
The present invention relates to the provision, use, maintenance, repair and reconstruction of energy efficient wall and closure systems that employ novel and improved panel assemblies of cast refractory and other insulating and support components for extending about selected peripheral portions of a thermal treatment chamber, with each panel assembly including an array of elongate cast refractory members 1) that extend side by side, 2) that have relatively wide flange portions that extend substantially contiguously to define a rigid, impact resistant inner surface that faces toward a thermal treatment chamber for absorbing, storing and re-radiating impingent heat energy back into the chamber, 3) that have relatively thin outer portions connected to the supporting frame, 4) that have central web portions that provide needed strength and rigidity while, at the same time, permitting only minimal conductive heat transfer therethrough, and 5) that have elongate, non-cast, fiber-type thermal insulating members compressively sandwiched between adjacent pairs of the cast refractory members for enhancing the panel's insulating capability while assisting the frame in supporting the panel's sandwiched array of insulating members. To provide panel assemblies that are optimally configured to meet the needs of a particular installation, the cross sections of the cast refractory members are optimally configured to desirably balance the need to minimize conductive heat transfer from inner to outer portions with other needs such as the need to provide strength and durability, the need to prevent the escape into the treatment chamber of fibrous refractory material, and the need to provide a relatively rigid, impact resistant inner surface that will efficiently absorb, store and re-radiate impingent heat energy. Also included within the purview of the present invention are a number of example forms of panel assemblies that employ cast sandwiched arrays of cast and fibrous refractory members, with the cast refractory members having web cross sections that minimize conductive heat transfer therethrough while also suitably balancing other needs.
2. Prior Art
In industry, high temperature furnaces of a wide variety of types are used to heat quantities of material that are to be used in manufacture. A high temperature industrial furnace typically includes wall and closure structures that extend about a thermal treatment chamber, with the wall and closure structures being formed from materials that will withstand the high temperatures to which they are exposed, and that will serve an insulating function so that outer surface portions of the walls and closures are maintained at significantly lower temperatures than are the inner surface portions thereof.
In many high temperature industrial furnace installations, it is important that the materials that are chosen to form the inner surface portions of wall and closure structures be capable of storing heat energy that is impingent on the inner surface portions, and of radiating heat energy back into the associated treatment chamber. Absent this heat storage and re-radiation capability, materials being heated in the treatment chamber will not be as evenly heated as desired for such material portions as are located near peripheral portions of the treatment chamber will receive less heat energy than will more centrally located material portions because heat that is impingent on inner wall surfaces will be absorbed rather than re-radiated back toward material portions that are located near the inner wall surfaces. A term used in industry to describe the effect that non-re-radiating inner wall surfaces have on the heating of objects that are located near such wall surfaces is "shadow effect"--a term intended to suggest that material portions positioned near a non-re-radiating inner wall surface will suffer uneven heating just as if it were placed within a "shadow" that is not properly radiated by heat energy that is being supplied to the treatment chamber.
Refractory brick often has been used to form at least significant portions of the inner surface structures of walls that surround the thermal treatment chambers of high temperature furnaces. While refractory brick is strong, resists physical abuse and has a capability to store impingent heat energy and to re-radiate stored heat energy back into a thermal treatment chamber, walls formed using brick are quite heavy, tend to deteriorate over time due to exposure to high temperatures within the range of 2000 to about 3000 degrees Fahrenheit, periodically need to be repaired and/or rebuilt, and typically need to be constructed relatively thickly in view of their somewhat less-than-desirable insulating characteristics.
Castable refractory material also has been used in various pre-fabricated forms and configurations to line or form component parts of wall and closure structures for use with high temperature industrial furnaces. Depending on the character and configuration of the materials that are used to form, reinforce and mount castable refractory members, such members can exhibit good strength and impact resistance characteristics, and can provide surface portions that will store and re-radiate heat energy. And, like refractory brick, appropriately formed castable refractory members can withstand exposure to high temperatures of up to about 3000 degrees Fahrenheit for reasonable periods of service before requiring repair and/or replacement.
As an alternative to the use of such rigid materials as refractory brick and cast refractory members, refractory fiber materials in bulk, bat and blanket form also have been proposed for use in forming wall and closure components for extending about peripheral portions of the thermal treatment chambers of high temperature furnaces and the like. While refractory fiber materials tend to exhibit significantly better insulating characteristics than do such rigid materials as refractory brick and cast refractory members, fiber refractory materials perform poorly when subjected to physical abuse, and tend to have an upper temperature limit for effective performance of about 2400 degrees Fahrenheit. While fiber refractory materials can physically withstand temperatures that are higher than about 2400 degrees Fahrenheit, a significant reason why such materials tend to fail to perform properly at temperatures above about 2400 degrees Fahrenheit is that steel anchoring materials and the like that need to be used to support and retain fiber refractory material in position tend to lose their requisite anchoring effect if fiber refractory materials are subjected to temperatures that extend beyond about 2400 degrees for significant periods of time.
In an effort to address the need for wall and closure structures that will make good use of such available materials as are described above, a number of the referenced Grandparent and Great Grandparent Cases, and the referenced Door Patents propose various composite barrier system approaches that are embodied in a variety of forms of insulated furnace door panels and the like. The approach taken in proposals of the Grandparent and Great Grandparent cases, and in proposals that have been made by others, is to make use of a "composite barrier system" that utilizes various combinations of solid (typically rigid), heat-storing-and-reradiating refractory materials together with fibrous (typically flexible), non-storing-and-non-reradiating materials to provide structures that are tailored to meet the needs of specific applications.
While the approach of utilizing various forms of "composite barrier systems" is known and has been used with success to meet various needs and requirements that are encountered in specific types of installations, the approach that typically has been used is to provide very different designs with each being tailored to address specific needs of a specific installation. What has not emerged is a single approach that has widespread applicability for use in designing and providing a versatile family of "composite barrier system products" that are optimized to meet specific needs without necessarily differing a great deal in structural configuration.
Turning to a more specific example of an application wherein needs of various types arise for wall and closure structures that are intended to minimize heat loss from high temperature industrial furnaces, in the steel industry it is well known to utilize what is referred to as a "reheat furnace" to sequentially heat large, preformed bodies of steel to desired temperatures to enable the heated bodies to be "worked" or otherwise formed, typically by rolling or by forging. A reheat furnace characteristically has a treatment chamber that is capable of receiving a plurality of large steel bodies such as slabs, billets or blooms of steel. The bodies of steel to be heated typically are fed through the treatment chamber relatively slowly in a direction of travel that extends from a closure controlled inlet or entry opening located on one side of the treatment chamber to a closure controlled outlet or exit opening located on an opposite side of the treatment chamber.
In a number of the referenced cases, the approach taken is to utilize a combination of cast refractory and fibrous refractory materials to define exposed inner surface portions of insulating panels, typically insulating panels that are used in the construction of inlet and/or outlet closures. While exposed fiber-type refractory bodies that are supported by exterior frame structures are well suited to serve the needs of furnace treatment chambers that operate at or below about 2,400 degrees Fahrenheit, present-day materials from which compressible fiber-type refractory bodies are formed tend not to provide insulated panel assemblies that are characterized by long service life if directly exposed for substantial periods of time to treatment chamber temperatures that exceed about 2,400 degrees Fahrenheit.
Other concerns also arise when fibrous refractory materials are used to define exposed inner surface areas of insulating panels of reheat furnaces and the like. One such concern is that, when relatively large interior surface areas of fiber-type refractory panels are exposed for significant periods of time to high temperature environments, there is a tendency for fibers from the refractory to become airborne. As a general rule, the greater the exposed surface area of fiber-type refractory, the greater is the concern that minuscule pieces of fiber may become airborne. Furthermore, the higher the temperature to which the refractory is exposed, the more rapidly the fiber-type refractory tends to deteriorate so as to present conditions that are increasingly susceptible to tiny pieces of fiber breaking away and becoming airborne.
Another concern (that inherently is present to some degree in almost all applications wherein fiber-type refractory material is used to form exposed interior wall portions of a high temperature treatment chamber) is the "shadow effect" problem described previously. Whereas wall portions that are formed from refractory brick function quite nicely to store and re-radiate impingent heat energy, wall portions formed from fibrous refractory do not. Thus, while re-radiation of heat energy from brick-lined walls will assist in maintaining nearby portions of steel bodies at desired high temperatures, exposed inner wall portions defined by fibrous refractory tend not to desirably re-radiate heat energy (and therefore tend to permit nearby portions of uniformly heated bodies of steel to cool undesirably, just as if a "shadow" had been cast over such portions to shield them from a source of heat energy).
The "shadow effect" problem is particularly acute when it is caused by fibrous refractory that forms interior surface areas of an exit closure of a steel reheat furnace, for bodies of steel that discharge from exit openings of reheat furnaces need to be in a uniformly heated state--not a state of non-uniform heat, which tends to occur if exit closures have exposed interior surface areas that are defined by fibrous refractory material. If the "shadow effect" of fiber-type refractory causes a slab of re-heated steel to lose its uniform working temperature, the heated slab may have to be shunted aside until it can be put through still another re-heat cycle.
3. The Parent Case
The invention of the referenced Parent Case had its origin in a continuing program of research and development that also has given rise to the invention of the present case. Thus it will be understood that both the invention of the Parent case and the invention of the present case have features that address similar objectives, namely the provision of frame-supported insulated panels for use in high temperature industrial furnaces and the like wherein the insulated panels 1) alleviate "shadow effect" concerns, 2) minimize airborne fiber concerns, and 3) function well in high temperature environments, for example in steel reheat furnaces wherein temperatures are maintained within the range of about 2400 to about 3000 degrees Fahrenheit.
Whereas features of the invention of the Parent Case call for the use of cast refractory members that are of "generally T-shaped cross section" (together with bodies of fibrous refractory material sandwiched between adjacent pairs of the cast refractory members) to form frame-supported insulated panels, features of the present invention define a broader and more diversified approach that can utilize cast refractory members of a variety of cross-sectional configurations (together with fibrous refractory material sandwiched between adjacent pairs of the cast refractory members) to form frame-supported insulated panels that alleviate "shadow effect" concerns, that minimize airborne fiber concerns, and that function well in high temperature environments, for example in steel reheat furnaces wherein temperatures are maintained within the range of about 2400 to about 3000 degrees Fahrenheit.